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ELECTRIC DRIVETRAIN TECHNOLOGIES

Introduction

The appeal of using electricity to power automobiles is that it would eliminate vehicular air pollution (although there would still be pollution at the power source), and that electricity can be reversibly translated to shaft power with precise control and high efficiency. The main problem with this use is that electricity cannot be easily stored on a vehicle.

California’s mandate for the introduction of zero emission vehicles in 1998 has resulted in a major research effort to overcome this storage problem. The only commercially available systems for storage today, however, are the lead acid and nickel-cadmium battery, and both have limited capabilities.

The lead acid battery’s limited storage capacity and substantial weight are ill-suited to a vehicle’s needs, although advanced versions of this battery reduce some of these limitations; the nickel-cadmium battery is very expensive and requires careful maintenance. Electricity can also be produced onboard a vehicle by using an engine and generator.

Simply feeding the generated electricity directly into a drive motor to power the wheels, however, would probably be less efficient than a mechanical transmission, because the combined generator and motor losses may outweigh transmission losses.

All about drive train

The total system can be made more efficient, however, if the engine is operated at near constant output close to its most efficient point, and any excess electricity is stored in a buffer, which is used to satisfy the variable electrical demands of the motor and other vehicle power demands. Vehicles with powertrains combining a device to store electrical energy and another to produce it are called hybrids.

The storage or buffer device can be an ultra-capacitor, flywheel, or battery, depending on system design; the electricity producer can be an internal combustion engine or, perhaps, a fuel cell, which would be both highly efficient and almost non-polluting. The sections that follow discuss new technology under development for batteries for electrical energy storage, fuel cells for energy production, capacitors/flywheels for peak power storage, and motors for conversion of electrical power to shaft power.

The discussions focus on a selected set of technologies likely to be competitive in the future marketplace (at least according to current wisdom), and their efficiency and cost characteristics. The data and descriptions presented in this section can become out-of-date very quickly, especially if there are breakthroughs in the design or manufacturability of the technologies.

Hence, the projections in this section represent an extrapolation of technology performance into the future based on information mail able as of 96 mid-1994. New technology competitors may emerge very quickly and new findings may render existing “competitive” technologies poor prospects for the future.

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